Natural gas compressors require a consistent supply of lubricant. To enter the compressor, the lubricant must be delivered at a pressure that is greater than the pressure within the compressor. Lubricant is typically distributed to the lubrication points by a divider block, which periodically delivers a small amount of lubricant at a high pressure to each lubrication point. A check valve is used to prevent hot gases from the compressor cylinder from flowing into the lubrication system when the pressure from the lubrication system is reduced, such as between cycles of the divider block. When the lubricant pressure is sufficiently high, the check valve opens and lubricant is injected into the compressor cylinder. When the lubricant pressure is reduced, the spring closes the valve to prevent gases from the compressor cylinder from entering the lubrication system.
Prior art check valves fail due to hot gas and debris entering the check valve each time the pump causes it to open to allow lubricant to be injected into the compressor cylinder or rod packing gland. The opening of the check valve exposes the seating surfaces to the hot gas and debris that are in the gas stream of the compressor. The hot gas heats the sealing surfaces in the check valve causing it to fail prematurely. The debris in the gas stream migrates into the check valve and causes the balls to stick open. As the debris lodges between the sealing surface and the ball, the hot gas migrates upstream into the lubricant tubing and causes problems with the pistons that inject oil into the cylinder or rod packing gland.
One known solution is a separate device, a check valve protector, installed on the downstream side of the check valve to protect the sealing surfaces. This solution adds extra cost to the components and adds another lubricant leak path to the system. Another disadvantage of current check valve protectors is the positioning of the lubricant inlet. The inlet is typically oriented at a 90-degree position from the check valve protector axis, which prevents the check valve protector from being installed in many applications where the cylinder is close to another cylinder. Another problem with prior art check valve protectors is that they incorporate a single NPT thread on the outlet. This can cause installation difficulties when installing the device. Due to the 90-degree inlet of this device, in many cases it must be over-torqued to position it correctly to align with the system tubing connection. This over-torquing causes extreme stress on the threads in the compressor cylinder, and has been known to destroy both the cylinder threads and the threads on the device. The over-torquing of the threads deforms the metal and not only causes issues with leaking explosive gases to the atmosphere, but also eliminates the ability to reuse that particular injection point if a new device has to be installed. When this occurs, the compressor cylinder must be removed and sent to a machine shop to be repaired or a new cylinder must be installed, which costs the owner/operator thousands of dollars.